The subject invention is directed toward the art of pipe joints and couplings and, more particularly, to an improved tube coupling. The coupling of the invention is particularly suited for use in ultra-high vacuum applications and will be described with reference thereto; however, it should be appreciated that the invention is capable of broader application and could be used in different fluid systems operating under a variety of conditions.
In U.S. Pat. No. 3,521,910 to Callahan, et al., there is disclosed a tube coupling which has achieved commercial success and is widely used in both pressure and vacuum operations. It finds widespread acceptance for use in ultra-high vacuum applications. The coupling of the noted patent generally comprises first and second annular coupling components having axial through passages and end faces which extend perpendicular to the axis of the passages. The end faces provide sealing surfaces for the coupling end and typically include an annular rib, or bead-like protuberance generally of hemispherical cross-section, which extends outwardly from each end face about the through passage. A smooth, flat annular metal sealing gasket is trapped between the opposed end faces. A threaded coupling nut or nuts act to drive the coupling components toward one another to produce sealing engagement of the annular ribs with opposite end faces of the annular sealing gasket.
During make-up of the coupling, it is highly preferable that relative rotation between the coupling components and the sealing washer be minimized. That is, it is desirable to suppress or eliminate any such relative motion which could produce undesirable scoring or galling of the sealing washer and/or the sealing end faces. Such scoring or galling can drastically reduce the effectiveness of the joint or produce undesired particles. In fact, under certain circumstances, leaks can develop and the ability to remake the joint after disassembly can be lost.
Various efforts have been proposed to prevent the relative rotation and reduce torque transmission from the coupling nut to one or the other of the coupling components. For example, U.S. Pat. No. 5,058,935, commonly owned and invented by the owner and inventor of the present application, discloses one manner of trying to suppress torque in coupling assemblies of this type. The disclosure of that patent is hereby incorporated by reference into the present application.
It has also been proposed to install anti-friction thrust bearings between the coupling nut and the associated coupling component. The driving forces from the coupling nut to the coupling components are thus directed through the thrust bearings. The intent is that the bearings transmit the axial make-up forces without the transmission of torque to the coupling components. Both standard and special ball and needle type thrust bearing assemblies have been used for this purpose. A commercial example of such an arrangement is the PURERING assembly sold by Fujikin Inc. in which the bearing ring is disposed over the gland and is axially interposed between the rear face of the gland and the radial shoulder of the female nut. Thus, torque is intended to be transferred to the bearing ring from the female nut, but not transferred to the coupling member, and likewise not transferred to the gasket. This arrangement, however, requires an enlarged nut to accommodate the bearing ring and the bearing ring is another component of the assembly that the user must handle.
Although the thrust bearing approach has been somewhat satisfactory, it is generally undesirable in that it significantly increases the cost and complexity of the coupling assemblies. Moreover, the addition of the anti-friction thrust bearings can significantly increase the overall length of the coupling assemblies. Accordingly, there has existed an ongoing need for a design to prevent relative rotary movement between the sealing faces of the coupling components and/or between the coupling components and the seal ring.
Another approach has been to use anti-torque prongs or interlocking tabs such as used in the Cajon S type VCR and the OmniSafe torque suppressors. These designs add complexity for the user and make them incompatible with existing VCR fittings already in use.